(11-25) 14:14 PST -- It's been a bloody Thanksgiving holiday for Bay Area residents, with at least five people killed on area highways while three members of another local family died in a grisly crash in the mountains outside Placerville.

A 23-year-old El Sobrante man was killed and a 21-year-old San Pablo man seriously injured early Sunday morning in a crash on westbound Highway 80 at the Cummings Skyway off-ramp in Crockett.

The victims, neither of whom was identified, were traveling "at a high rate of speed" when their 2005 BMW slammed into the back of a big rig truck and burst into flames, according to a California Highway Patrol report. Neither the driver nor the passenger in the truck was injured. All lanes of westbound 80 were closed for a time, with all lanes reopened shortly after 5 a.m.

An unidentified woman was struck and killed by a hit-and-run driver sometime after 8 p.m. Saturday as she apparently was standing on Highway 101 near the Oyster Point Boulevard off-ramp in South San Francisco.

The victim was struck by several other vehicles before CHP officers arrived on the scene. Investigators are seeking the car that originally struck the woman, as well as trying to determine the victim's identity and why she was on or alongside the freeway.

Northbound Highway 101 was closed for more than two hours.

A 59-year-old San Jose man was killed at about 9 p.m. Saturday night when his car, traveling the wrong way on the San Tomas Expressway in San Jose, collided with another car, north of Williams Road. The driver of the other car was hospitalized with unknown injuries.

Also on Saturday night, four people were killed and five injured in head-on collision Highway 50, just outside Placerville in El Dorado County.

Three of the victims are members of a Bay Area family, but investigators still are trying to determine what city they are from.

"It was an accident with no witnesses, so it's taking time to get the information together," said Sgt. Jim Byers of the El Dorado County Sheriff's Department. "There are also significant language issues with the family of the people from outside our area."

The Bay Area family was traveling west in a Toyota Prius shortly after 6 p.m. when their vehicle suddenly crossed the center stripe and slammed head-on into a minivan headed east.

The driver of the Prius, a 39-year-old man, was killed in the collision, along with an adult woman and a child. A 10-year-old in the car was treated for minor injuries.

A four-year-old girl riding in the minivan was killed and an adult passenger is listed in critical condition at a Sacramento-area hospital, Byers said. Three others, including a pair of 1-year-old twins, suffered minor injuries.

On Friday, two San Bruno sisters in their 20s were killed when their family's Lexus SUV sideswiped a CHP vehicle on Highway 101 near the Oregon Expressway in Palo Alto. Four other members of the family were hospitalized after the crash.

The bloodbath on Northern California roads came as the CHP put on a maximum enforcement period for the holidays, boosting their presence along state freeways from 6 p.m. Wednesday, the day before Thanksgiving, until midnight Sunday.

So far, the focused enforcement hasn't made a dent in the number of people killed on the road. As of midnight Saturday, the CHP reported more traffic fatalities, both in the Bay Area and statewide, than there were last year, although the number of drunk driving arrests has gone down.

Through Saturday, 31 people already had died in collisions on California highways, up from 21 during the same period last year, according to CHP statistics. That's just under the 32 people killed over the entire 2011 Thanksgiving holiday, which was a 50 percent increase from 2010.